According to the New York Times, "Studies Find That for Men, It Pays to Be Married." Economists "drew on a unique data set, the Minnesota Twins Registry, which tracked most twins born in Minnesota between 1936 and 1955 . . . They found that the married men in their sample earned about 19% more than the unmarried men . . . They found that married twins had 26% higher wages than their unmarried siblings."31
a. Did the first result (19% more) come about from a paired or a two-sample design?
b. Did the second result (26% higher) come about from a paired or a two-sample design?
c. Explain how it is possible that causation may occur in the opposite direction from what the title suggests.